1. Field of the Invention
The present invention relates to a detent device for maintaining a control lever at an operating position which issues a command of a winding-up or other to a winch of a crane or the like.
2. Prior Art
As a conventional detent device for a control lever, the device shown in FIG. 6 is well known. The well known example shows the case where the device is applied to a so-called remote control valve in which a pilot reducing valve is actuated by operation of a lever.
In FIG. 6, the reference numeral 1 designates a control lever, and 2 is a cam secured to the control lever 1, these being integrally rotated around a horizontal shaft 3. Push rods 4a and 5a of pilot reducing valves 4 and 5 come into contact with the bottom surface of the cam 2 so that one of the reducing valves 4 and 5 is actuated by rotation of the cam 2 and a main control valve not shown is switched by the secondary pressure thereof and the winding-up or winding-down operation is carried out.
Both sides 2a, 2a (hereinafter referred to as cam surfaces) of the cam 2 are provided with detent recesses 6 . . . at two locations corresponding to operating positions (detent positions) on both sides of the lever. A piston case 8 is provided on a housing 7 housing therein the cam 2, the piston case 8 being interiorly provided with a piston 9 and a bias spring 10 for biasing the piston 9 toward the cam surface 2a. A ball 11 in elastic contact with the cam surface 2a is held on the end of the piston 9, and at the detent position. The ball 11 is engaged with the recess 6 of the cam 2 whereby the cam 2, that is the control lever is held at the detent position against the spring reaction of the reducing valves 4 or 5.
However, in the aforesaid prior art, the ball 11 is always in contact with the cam surface 2a with a fixed spring force, and this spring force is relatively great enough to hold the control lever 1 at the detent position overcoming the reaction of the reducing valve. Therefore, there is an unpleasant feeling of resistance during the operation of the lever, and the operating feeling is poor and the lever operation becomes unduly heavy.
In the control lever for controlling a winch for a crane, operating reaction is increased as a load (a lifting load) increases, and therefore, load pressure or the like of an actuator (hydraulic motor) is applied as a lever operating reaction to the control lever 1, as disclosed in Japanese Utility Model Application Laid-Open No. 14199/1980. In this case, according to the prior art, a proportion of load reaction occupied by the entire operating reaction decreases as the result of great operating resistance (hereinafter referred to as detent resistance) caused by the detent device, which gives rise to a problem in that the load reaction is hard to be transmitted to a driver.